1. Field of the Invention
This invention relates to collison detectors and more particularly to an automatic system of collision detection for an automobile including safety devices which may be actuated in case of an impact.
2. Description of the Prior Art
Conventional shock sensors are generally made up of a inertial mass which is pulled toward the vehicle by the working of a return force, for example, a magnetic force or a drawback spring. The inertial mass travels in the direction of the acceleration it measures and upon the occurrence of a strong shock, strikes against a device which delivers an electrical signal. This device may produce the signal by establishing contact between two wires, for example. The inconvenience of this type of sensor is in the difficulty of testing the sensor's functioning during the vehicle's movement in the absence of shock, and in the impossibility of using the same sensor to operate diverse apparatus which would have to be set in motion independently for atypical shocks.
With certain devices of the prior art, the testing of a sensor's proper functioning is effected by measuring a parameter which is not the signal directly delivered by the sensor. This procedure is not sufficiently reliable. Indeed, an accelerometer including a force gauge attached to a vibrating blade can present a normal resistance and yet not give a signal. This can happen if the gauge becomes detached under the effect of the vehicle's vibrations. The same would be the case for a piezo-electrical sensor if its capacity were to be measured.